Element mapping unit, scanning transmission electron microscope, and element mapping method

Abstract

There is provided an element mapping unit, scanning transmission electron microscope, and element mapping method that enable to acquire an element mapping image very easily. On the scanning transmission electron microscope, the electron beam transmitted through an object to be analyzed enters into the element mapping unit. The electron beam is analyzed of its energy into spectrum by an electron spectrometer and an electron energy loss spectrum is acquired. Because the acceleration voltage data for each element and window data for 2-window method, 3-window method or contrast tuning method are already stored in a database and accordingly the spectrum measurement is carried out immediately even when an element to be analyzed is changed to another, the operator can confirm a two-dimensional element distribution map immediately. Besides, because every electron beam that enters into an energy filter passes through the object point, aberration strain in the electron spectrometer can be minimized and higher energy stability can be achieved. As a result, drift of the electron energy loss spectrum acquired by analyzing the electron beam into spectrum can be minimized and element distribution with higher accuracy can be acquired.

1. A scanning transmission electron microscope comprising:
 an electron beam source to generate electron beams; 
 a scanning section to scan the electron beam; 
 objective lens to converge the electron beam onto a specimen; 
 an electron spectrometer that analyzes into spectrum the energy of the electron beam transmitted through the specimen, the electron spectrometer having an accelerating tube to accelerate the electron beam; 
 a plurality of electron beam detectors that are capable of a simultaneous measuring of at least two energy ranges of spectra for the electron beam that lost specific energy; 
 a storage device which stores acceleration voltage data and window information for different elements to be analyzed; 
 an input device to select a measurement region and an element to be analyzed; and 
 a control unit that controls the accelerating tube so that the electron beam, which has lost specific energy corresponding to a selected element to be analyzed, enters into a fixed position in the electron beam detectors, based on the data stored in the storage device; and detects the selected element to be analyzed on the basis of the intensity of the electron beam within a predetermined energy range out of those electron beam intensities detected above; distribution images of different elements being obtained by switching objective elements at a same measurement region during observation of one specimen. 
 
     
     
       2. A scanning transmission electron microscope according to  claim 1 , wherein
 the control unit contains a storage section that stores in memory the acceleration voltage for accelerating the electron beam that has lost specific energy and the energy range of the electron beam to be used for detecting the element to be analyzed; and 
 a computation section that detects the element to be analyzed using the electron beam intensity within the afore-mentioned energy range stored previously. 
 
     
     
       3. A scanning transmission electron microscope according to  claim 2 , wherein
 the storage section stores correction data for eliminating the effect peculiar to the electron beam detectors from the detected electron beam; and 
 the computation section corrects the detected electron beam in accordance with the correction data. 
 
     
     
       4. A scanning transmission electron microscope according to  claim 2 , wherein
 the electron beam detectors contain multiple electron beam detecting sections corresponding to the electron beam energy; 
 the storage section stores the 1 st  energy range, which is a range including the core loss peak, and the 2 nd  energy range, which is a range lower than the core loss peak, out of an inner shell electron energy loss spectrum of the element to be analyzed; 
 the control unit detects the 1 st  electron beam intensity detected by the electron beam detecting section corresponding to the 1 st  energy range and the 2 nd  electron beam intensity detected by the electron beam detecting section corresponding to the 2 nd  energy range on the basis of the stored 1 st  energy range and 2 nd  energy range; 
 the computation section divides the 1 st  electron beam intensity by the 2 nd  electron beam intensity so as to detect the element to be analyzed. 
 
     
     
       5. A scanning transmission electron microscope according to  claim 2 , wherein
 the electron beam detectors contain multiple electron beam detecting sections corresponding to the electron beam energy; 
 the storage section stores the 1 st  energy range, which is a range including the core loss peak, and the 2 nd  and 3 rd  energy ranges, which are two ranges each lower than the core loss peak, out of an inner shell electron energy loss spectrum of the element to be analyzed; 
 the control unit detects the 1 st  electron beam intensity detected by the electron beam detecting section corresponding to the first energy range, 2 nd  electron beam intensity detected by the electron beam detecting section corresponding to the 2 nd  energy range, and 3 rd  electron beam intensity detected by the electron beam detecting section corresponding to the 3 rd  energy range on the basis of the stored 1 st  energy range, 2 nd  energy range, and 3 rd  energy range; 
 the computation section acquires the background intensity of the 1 st  energy range in accordance with the 2 nd  electron beam intensity and 3 rd  electron beam intensity, and calculates the difference between the 1 st  energy range and the acquired background intensity so as to detect the element to be analyzed. 
 
     
     
       6. A scanning transmission electron microscope according to  claim 2 , wherein
 the electron beam detectors contain multiple electron beam detecting sections corresponding to the electron beam energy; 
 the storage section stores the plasmon energy range including the plasmon peak out of the inner shell electron energy loss spectrum of the element to be analyzed; 
 the control unit detects the plasmon loss intensity of the electron beam detected by the electron beam detectors corresponding to the plasmon energy range on the basis of the stored plasmon loss energy range; and 
 the computation section detects the element to be analyzed on the basis of the detected plasmon loss intensity. 
 
     
     
       7. A scanning transmission electron microscope according to  claim 1 , wherein
 the control unit controls the accelerating tube so that the 1 st  electron beam, which has lost specific energy corresponding to the 1 st  element to be analyzed, enters into a fixed position in the electron beam detectors; 
 detects the 1 st  element on the basis of the 1 st  electron beam intensity in a predetermined energy range out of the detected 1 st  electron beam intensities; 
 when the second element to be analyzed is inputted from the outside, 
 controls the accelerating tube so that the 2 nd  electron beam, which has lost specific energy corresponding to the 2 nd  element to be analyzed, enters into a fixed position in the electron beam detectors, and 
 detects the 2 nd  element on the basis of the 2 nd  electron beam intensity in a predetermined energy range out of the detected 2 nd  electron beam intensities. 
 
     
     
       8. An element mapping method that generates a distribution image of an element contained in an object to be analyzed on the basis of the energy spectrum of an electron beam transmitted through the object to be analyzed and the irradiation position of the electron beam on the object to be analyzed; including
 scanning irradiated electron beams onto the object to be analyzed; 
 accelerating the electron beam transmitted through the object to be analyzed; 
 analyzing into spectrum the energy of the electron beam transmitted through the object to be analyzed; 
 detecting the intensity of the electron beam by a plurality of electron beam detectors, the detectors are capable of a simultaneous measuring of at least two energy ranges of spectra for the electron beam that lost specific energy; 
 retrieving from a storage device acceleration voltage data and window information for an element to be analyzed; 
 detecting the element to be analyzed on the basis of the electron beam intensity; 
 moving the position of the electron beams to be irradiated onto the object to be analyzed; wherein
 the acceleration includes accelerating the electron beam so that the electron beam, which has lost specific energy corresponding to the element to be analyzed, enters into a fixed position in the electron beam detectors, based on the data retrieved from the storage device; and 
 the detecting the element includes detecting the element to be analyzed on the basis of the intensity of the electron beam within a predetermined energy range out of those electron beam intensities detected above; 
 
 accepting an input to select another element to be analyzed for a same measurement region; and 
 switching to the other element to be analyzed to obtain distribution images for the element and the other element at the same measurement region. 
 
     
     
       9. An element mapping method according to  claim 8 , wherein switching the element to be analyzed to the other element includes:
 accelerating the electron beam so that the electron beam, which has lost specific energy corresponding to the other element, enters into a fixed position in the electron beam detectors; and 
 detecting the other element to be analyzed on the basis of the intensity of the electron beam within a predetermined energy range corresponding to the other element out of those electron beam intensities that are detected when the electron beam, which has lost specific energy corresponding to the other element, enter into the electron beam detectors.